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AR# 30626: IP-DSP - Why are there mismatches between the behavioral simulation and the post-translate simulation when using ISE Simulator, NC-Sim with the CIC Compiler, DDS Compiler, or the Sine CoSine LUT IP?

AR# 30626

IP-DSP - Why are there mismatches between the behavioral simulation and the post-translate simulation when using ISE Simulator, NC-Sim with the CIC Compiler, DDS Compiler, or the Sine CoSine LUT IP?

Description

Why are there mismatches between the behavioral simulation and the post-translate simulation, when using ISE Simulator, NC-Sim with the CIC Compiler, DDS Compiler, or the Sine CoSine LUT IP?

Also, why do these mismatches not occur when I use ModelSim?

Solution

This issue is caused by a float to integer conversion function that is used in the behavioral model for the following list of cores. The IEEE standard for this function can be interpreted in multiple ways. Consequently, there are differences in how the rounding is performed, depending on which simulator is used. These cores work as expected in ModelSim, but not in ISE Simulator or NC-Sim.